Syndiotactic 1,2-polybutadiene is a very valuable material for use in the manufacture of food films. Methods for the synthesis of this polymer by polymerizing 1,3-butadiene monomer in hydrocarbon or halogenated hydrocarbon solvents are well-known.
A process for the preparation of 1,2-polybutadiene which comprises polymerizing 1,3-butadiene in the liquid phase, in the presence of a catalyst composition composed of:
(a) a cobalt compound PA1 (b) an organoaluminum compound of the formula EQU AlR.sub.3 PA1 in which R is a hydrocarbon radical of 1-6 carbons, and PA1 (c) carbon disulfide PA1 i. .beta.-diketone complexes of cobalt; PA1 ii. .beta.-keto acid ester complexes of cobalt; PA1 iii. cobalt salts of organic carboxylic acid having 1 to 25 carbon atoms, and PA1 iv. complexes of halogenated cobalt compounds of the formula: CoX.sub.n wherein X represents a halogen atom and n represents 2 or 3, with an organic compound selected from the group consisting of tertiary amines, alcohols, tertiary phosphines, ketones and N,N-dialkylamides.
is disclosed in U.S. Pat. No. 3,778,424, which is herein incorporated by reference in its entirety. U.S. Pat. No. 3,901,868 reveals a process for producing a butadiene polymer consisting essentially of syndiotactic 1,2-polybutadiene by the successive steps of:
(a) preparing a catalyst component solution by dissolving, in an inert organic solvent containing 1,3-butadiene, a cobalt compound, soluble in the organic solvent, such as (i) cobalt-.beta.-diketone complex, (ii) cobalt-.beta.-keto acid ester complex, (iii) cobalt salt of organic carboxylic acid, and (iv) halogenated cobalt-ligand compound complex, and an organoaluminum compound,
(b) preparing a catalyst composition by mixing the catalyst component solution with an alcohol, ketone or aldehyde compound and carbon disulfide,
(c) providing a polymerization mixture containing desired amounts of 1,3-butadiene, the catalyst composition and an inert organic solvent, and
(d) polymerizing 1,3-butadiene at a temperature of -20.degree. C. to 90.degree. C. This patent is herein incorporated by reference in its entirety.
U.S. Pat. No. 3,901,868 indicates that the polymerization of 1,3-butadiene into syndiotactic 1,2-polybutadiene must be conducted in an inert organic solvent. The term inert organic solvent as used in U.S. Pat. No. 3,901,868 refers to an organic solvent chemically inert to all of the catalyst components used in the process of the present invention, 1,3-butadiene and the butadiene polymer. Some representative examples of inert organic solvents include aromatic hydrocarbons, aliphatic hydrocarbons, alicyclic hydrocarbons, most halogenated hydrocarbons, and mixtures of two or more of the above-mentioned compounds. The aromatic hydrocarbons may be benzene, toluene, xylenes, -ethylbenzene, diethylbenzene or isobutylbenzene; and the aliphatic hydrocarbons may be n-hexane, isohexanes, n-heptane, n-octane, isooctanes, n-decane, 2,2-dimethylbutane, petroleum ether, kerosene, petroleum spirit or petroleum naphtha, and the alicyclic hydrocarbon may be either cyclohexane or methylcyclohexane. Some representative examples of inert halogenated hydrocarbons are chlorobenzene and methylene chloride. Unfortunately, these inert organic solvents are toxic and extensive solvent removal procedures are required to remove them from polymers that are used in food-wrap films.
Obviously, the synthesis of syndiotactic 1,2-polybutadiene in a solvent that is less toxic would be very desirable. However, it has been the rule that less toxic solvents are not inert and will destroy the catalyst being used in the polymerization. For example, it is well-known that water will destroy the organoaluminum catalyst component used in such a polymerization.
It would be very desirable to use tetrahydrofuran as the polymerization medium for the synthesis of syndiotactic 1,2-polybutadiene which is used in articles for packaging, transporting or storing of foods since it is less toxic and is allowable at higher residual levels than other more toxic solvents. The problem with tetrahydrofuran is that it is not an inert organic solvent. If it is used as the solvent in such a polymerization, polymer yields will be reduced to unacceptable levels for commercial applications unless the catalyst is protected from the tetrahydrofuran by using the procedure described herein.